Monoxide Molar Ratio Research Articles

Response surface modelling of biomass-rich municipal solid waste pyrolysis: towards optimum hydrogen production

In this study, two-step pyrolysis of biomass-rich municipal solid waste was studied on nickel supported ZSM-5 catalyst. In the first stage of the reactor, constant temperature (T = 550 °C) was applied, and in the second stage, the reactions took place at 500, 700 and 850 °C. Effects of operating parameters (temperature = 500, 700, 850 °C, steam rate = 1, 5 g/h) and catalyst load (0.5, 1.0, 2.0) were studied on yields and compositions, particularly on the hydrogen contents. In order to determine the significance of the operating parameters, response surface methodology was used. Considering the experimental data, the values of hydrogen/carbon monoxide molar ratio, lower heating value and the simulation, it was found that the favourable operating parameters of two-step pyrolysis of biomass-rich municipal solid waste were 850 °C temperature and 1 g/h steam rate (gas yield: 27.1%, hydrogen yield: 9.96 mmol g−1 waste, hydrogen/carbon monoxide molar ratio: 1.8). From the data of response surface methodology, it was also concluded that temperature has a more critical effect on gas yields and composition than steam rate. However, in some cases, the synergistic effect of the two factors can also be significant.Graphical abstract

High-quality syngas production from biomass driven by chemical looping on a PY-GA coupled reactor

A suitable reactor for high-quality syngas production was crucial for the biomass gasification process. In this study, a pyrolysis-gasification (PY-GA) coupled reactor was designed, built-up and studied for producing hydrogen rich syngas with low tar containing. The experiment of the chemical looping gasification (CLG) process combined with biomass pyrolysis was conducted, regarding as the influence of different temperatures and steam to biomass mass ratios (S/B ratios). The gas composition from the outlets of the reactor, carbon conversion efficiency, lower heating value (LHV) of gas, syngas yield, and cold gas efficiency (CGE) were calculated and evaluated. The hydrogen to carbon monoxide molar ratio (H2/CO ratio) and the tar yield were compared with other similar technologies, and the possible reaction steps for high-quality syngas were finally discussed. The results showed that H2 composition in the GA part could reach over 61%. The total carbon conversion efficiency could reach 99.08%, and the CGE of the production was at range of 46–61%. Comparing with some similar gasification technologies, the obtained H2/CO ratio was over 3.47 mol/mol (820 °C and 1.0 kg/kg), and the whole process produced little tar during the reactions. The study provided with a novel method to take place the pyrolysis and gasification reactions in different reactors.

Simulation and Optimization of Coal Gasification in a Moving-bed Reactor to Produce Synthesis Gas Suitable for Methanol Production Unit

This paper presents process simulation and optimization of coal gasification process<br /> in a moving-bed reactor using Pittsburgh No. 8 coal as feed. The system of differential<br /> equations for the mass and energy balances was solved using 4th-order Runge-Kutta method and optimized by non-dominated sorting genetic algorithm-II (NSGA-II) method.<br /> The simulation was used to predict solid and gas temperature profile and gas composition<br /> along the reactor. The simulation results were compared successfully with experimental<br /> data relevant to Westfield plant in Scotland. In addition, the effect of operating parameters such as coal-to-oxygen molar ratio, steam-to-oxygen molar ratio, inlet gas temperature, reactor pressure, and oxygen mole fraction in inlet air on amount of synthesis gas (syngas) production, hydrogen to carbon monoxide molar ratio (HCMR) in produced syngas, and coal conversion was investigated. Finally, the reactor performance was optimized to produce the highest syngas production with a HCMR of two using NSGA-II method.

Chemical looping pyrolysis-gasification of biomass for high H2/CO syngas production

Chemical Looping Pyrolysis-Gasification (CLPG) of biomass is established as a novel concept for high quality syngas production. The process divides the main chemical reactions in different zones for biomass pyrolysis and gasification, then achieves residual char combustion and Oxygen Carrier (OC) regeneration consistently. The understanding of the process is first determined by calculation of possible chemical reactions using Gibbs Free Energy (ΔG). Experimental work for different effects of the fuel reactor (FR) temperature and the Steam-to-Biomass Mass Ratio (S/B) are then investigated in terms of syngas components, Hydrogen to Carbon Monoxide Molar Ratio (H2/CO), and Cold Gas Efficiency (CGE). Results show that at the FR temperature of 820°C and S/B of 1.00kgkg−1, the optimized condition of H2/CO and CGE are obtained at 2.45molmol−1 and 61.87%, respectively. With S/B increasing from 1.25kgkg−1 to 2.00kgkg−1, the H2/CO increases to 2.99kgkg−1, while the CGE decreases to 51.64%. The water-gas shift (WGS) reaction and the steam-iron reaction are approaching 0kJmol−1 over the FR temperature of 820°C in calculation, which confirms the contribution of these two reactions comparing with experimental tests. The research proposes an approach for efficient gasification of high volatile-content solid fuel using the advanced chemical looping technology.

Evaluation of nickel and copper catalysts in biogas reforming for hydrogen production in SOFC

The solid oxide fuel cells (SOFC) enable the efficient generation of clean energy, fitting the current requirements of the growing demand for electricity and for the environment preservation. When powered with biogas (from digesters of municipal wastes), the SOFCs also contribute to reduce the environmental impact of these wastes. The most suitable route to produce hydrogen inside SOFC from biogas is through dry reforming but the catalyst is easily deactivated by coke, because of the high amounts of carbon in the stream. A promising way to overcome this drawback is by adding a second metal to nickel-based catalysts. Aiming to obtain active, selective and stable catalysts for biogas dry reforming, solids based on nickel (15%) and copper (5%) supported on aluminum and magnesium oxide were studied in this work. Samples were prepared by impregnating the support with nickel and copper nitrate, followed by calcination at 500, 600 and 800 oC. It was noted that all solids were made of nickel oxide, nickel aluminate and magnesium aluminate but no copper compound was found. The specific surface areas did not changed with calcination temperature but the nickel oxide average particles size increased. The solids reducibility decreased with increasing temperature. All catalysts were active in methane dry reforming, leading to similar conversions but different selectivities to hydrogen and different activities in water gas shift reaction (WGSR). This behavior was assigned to different interactions between nickel and copper, at different calcination temperatures. All catalysts were active in WGSR, decreasing the hydrogen to carbon monoxide molar ratio and producing water. The catalyst calcined at 500 oC was the most promising one, leading to the highest hydrogen yield, besides the advantage of being produced at the lowest calcination temperature, requiring less energy in its preparation.

Analysis of di-methyl ether production routes: Process performance evaluations at various syngas compositions

This paper investigates direct di-methyl ether (DME) production based on dry methane reforming (DMR-to-DME) and on bireforming (BiR-to-DME). Technically, DMR-to-DME is preferred to BiR-to-DME because the former produces synthesis gas (syngas) with a hydrogen to carbon monoxide molar ratio (H2/CO) of 1 which is the ideal ratio for DME synthesis. Whereas the latter produces a H2/CO close to 2 and consequently suffers from two apparent drawbacks: (1) lack of the so-called ‘synergy effect’ – a feature that enhances DME yield when operating at H2/CO close to 1, and (2) generation of a high heat capacity by-product (H2O) which makes DME recovery energy intensive. In this paper, we find that those two disadvantages actually enhance the performance of BiR compared to DMR across a range of performance metrics. Although the presence of water increases the cooling/heating duty and the distillation columns’ reboiler duty in the BiR route, more heat released from DME synthesis reactor can be utilized in the reboilers to make BiR techno-economically compatible. To assess the sustainability of DMR and BiR, evaluations are carried out against an existing industrial scale DME production route (auto-thermal-reforming (ATR)). By utilizing the carbon in the CO2 from an attached post-combustion carbon capture plant, DMR and BiR can save 22.3% methane feed uptake on average compared to the ATR process, which results in the DMR and BiR reducing CO2 emissions by at least 6.5% on average.

Steam reforming of biogas over a Rh/Al2O3 catalyst in an annular microreactor

The article deals with the catalytic steam reforming of biogas of model composition into hydrogen and carbon monoxide over a Rh/γ-Al2O3 catalyst in an annular microchannel reactor. The reforming of biogas consisting of 60% methane and 40% carbon dioxide in a steam medium has been experimentally investigated under isothermal conditions while activating the reactions on the inner convex wall of the annular microchannel with a thin catalyst layer. The experiments have been performed at a residence time of 0.12 s, reactor temperatures of 750 and 860°C, and a water: biogas molar ratio of 0.8 to 3.1 in the feed. The range of water: biogas molar ratios maximizing the hydrogen yield has been determined for the model biogas. By changing the reactor temperature and water: biogas molar ratio, it is possible to widely vary the hydrogen: carbon monoxide molar ratio in the resulting synthesis gas.

Novel supports for nickel-based catalysts for the partial oxidation of methane

Zirconia-supported nickel catalysts with different amounts of aluminum (Al/Zr = 0.2, 1 and 2) were studied in this work in order to find alternative supports for nickel-based catalysts for the partial oxidation of methane. This reaction is a promising route for producing hydrogen and syngas for different applications. Samples were prepared by precipitation and impregnation techniques, characterized by several techniques and evaluated in the partial oxidation of methane in the range of 450–750 °C and 1 atm. It was found that aluminum affects the textural and catalytic properties of zirconia-supported nickel catalysts. The tetragonal phase of zirconia was stabilized by aluminum and gamma-alumina was also found in the aluminum-richest samples. Aluminum increased the porosity and the specific surface area of the solids. The catalytic activity also increased with the amount of aluminum in solids probably due to the stronger interaction of nickel with the support, which slowly generates active sites during the reduction step. The methane conversion and hydrogen selectivity increased with temperature, indicating no deactivation. The hydrogen to carbon monoxide molar ratio decreased due to aluminum but was not significantly affected by temperature. The coke produced was not harmful to the catalysts and aluminum affected its amount, although no simple relationship was found between these parameters. The most promising catalyst was the sample with aluminum to zirconium molar ratio of 2, which showed high activity and hydrogen selectivity and was stable under the reaction condition.

System Analysis of Nuclear-Assisted Syngas Production From Coal

A system analysis has been performed to assess the efficiency and carbon utilization of a nuclear-assisted coal gasification process. The nuclear reactor is a high-temperature helium-cooled reactor that is used primarily to provide power for hydrogen production via high-temperature electrolysis. The supplemental hydrogen is mixed with the outlet stream from an oxygen-blown coal gasifier to produce a hydrogen-rich gas mixture, allowing most of the carbon dioxide to be converted into carbon monoxide, with enough excess hydrogen to produce a syngas product stream with a hydrogen/carbon monoxide molar ratio of about 2:1. Oxygen for the gasifier is also provided by the high-temperature electrolysis process. The results of the analysis predict 90.5% carbon utilization with a syngas production efficiency (defined as the ratio of the heating value of the produced syngas to the sum of the heating value of the coal plus the high-temperature reactor heat input) of 64.4% at a gasifier temperature of 1866 K for the high-moisture-content lignite coal considered. Usage of lower moisture coals such as bituminous can yield carbon utilization approaching 100% and 70% syngas production efficiency.

Preparation and characterization of Ru/MgO-Al 2O 3 catalysts for methane steam reforming

The preparation and characterization of aluminum and magnesium oxides-supported ruthenium were described in this work, aiming to compare different supports to methane steam reforming catalysts for producing hydrogen. Gama-alumina-supported ruthenium and periclase-supported ruthenium were produced. The addition of small amounts of magnesium to alumina-supported ruthenium in the range of Mg/Al (molar) = 0.2–0.5 did not change the gama-alumina structure while high amounts (Mg/Al (molar) = 5) led to the production of periclase. Magnesium caused a decrease of specific surface area of alumina-supported ruthenium catalysts and this effect increased with the amount of the metal in solids. Magnesium also decreased the acidity of alumina-supported ruthenium and generated electron deficient ruthenium species, besides increasing their interaction with the support. The addition of magnesium increased the ruthenium dispersion but did not increase the methane conversion, suggesting that it negatively changed the electron properties of ruthenium towards methane conversion. However, it avoided deactivation during reaction and changed the activity for the water gas shift reaction, allowing tailoring the hydrogen to carbon monoxide molar ratio. The catalysts showed activity close or higher than a commercial sample, indicating that they are promising for the reaction, with the advantage that it can be tailored for several applications.

Reduction of nitrogen oxide by carbon monoxide over pure and platinum-doped LaMnO3 perovskites. Effect of oxygen on the reaction

The reduction of NO by CO has been studied using pure and platinum-doped LaMnO3 perovskites as catalysts. The reaction products always include nitrogen monoxide, whose amount varies with temperature. The reaction kinetics for the two catalysts are different and have been described by different rate laws. Considerable differences have also been found in the apparent activation energies: in the presence of Pt it is about half that for the reaction catalyzed by pure LaMnO3. Both the catalysts exhibit good catalytic properties, but the platinum-doped LaMnO3 shows a higher catalytic activity. The presence of oxygen in the inlet mixture affects considerably the kinetics of the reaction catalyzed by platinum-doped LaMnO3. The conversion of NO passes through a maximum at an oxygen/carbon monoxide molar ratio, m, of 1.8. At m > 1.8, CO is oxidized preferentially by oxygen rather than by NO.

On the determination of kinetic parameters for the regeneration of cracking catalyst

AbstractIn the study of the regeneration of cracking catalyst, two approaches may be taken when determining the kinetic rate constant for the coke combustion reaction. A global coke burning rate equation may be considered, based on the observed oxygen concentration and carbon dioxide to carbon monoxide molar product ratio. This reaction may also be represented by an intrinsic coke burning equation which is a function of the oxygen concentration and the carbon dioxide to carbon monoxide molar ratio at the reaction site, combined with a carbon monoxide postcombustion equation. It is proposed in this paper that the rate constant for intrinsic coke burning, kc, is essentially equal to the global coke burning rate constant, kc, and that its value is independent of the rate equation chosen for the carbon monoxide post‐combustion reaction.